It is well recognized that following bilateral ablation of the caudal pontile pneumotaxic center and bilateral vagal section, apneusis is obtained. In apneusis, the periods of phrenic nerve activity and inactivity are of many minutes duration. We are interested in examining the processes which might underlie the termination of these exceedingly long inspiratory and expiratory periods. Preliminary results have established that a variety of non-specific stimuli, including sciatic nerve stimulation or sound, can terminate the inspiratory and expiratory phases of apneusis. Experiments to quantify such effective stimuli are planned. A second series of experiments will examine whether voluntary ventilatory mechanisms of cerebral cortical origin and brainstem automatic ventilatory control systems are interactive at brainstem sites. As a first step in these experiments, an anesthetic regiment which does not suppress activities of pontile respiratory neurons had to be found. Experiments to date have established that chloralose-urethane may fulfill this required criterion.